Keratinocytes from uninjured skin express specific patterns of genes that promote proliferation and differentiation. In injuries disrupting the basement membrane (BM), wound edge keratinocytes contract dermal extracellular matrix (ECM) and are activated to global changes in gene expression, switching from a proliferation /differentiation program to one supporting re-epithelialization and repair of the tissue defect. Factors that induce keratinocyte activation following injury, whether soluble or matrix, remain to be fully elucidated. Type I collagen may play an important role in keratinocyte activation in wounds that disrupt the BM. Indeed, when keratinocytes from intact skin are plated onto activated keratinocytes at the wound edge essential for migration across the denuded dermis. Differential display RT-PCR identified 3 distinct classes of transcripts: (1) known genes associated with keratinocyte differentiation, (2) known genes not previously described in skin, and (3) novel transcripts. These data indict that keratinocytes are stimulated to express several transcripts following contact with type I collagen and that cell:ECM interaction is a critical determinant for cell activation upon wounding. cDNA clone GAP4G1, a novel transcript that was markedly induced (20-fold), was sequenced and found to have 100% identity to nucleotides 10237-10379 of human chromosome 17 clone hCIT.22_K_21. Subsequent amplification and translation of the full- length cDNA revealed epsin 3, a novel 632 amino acid protein closely related to, but distinct from members of the epsin protein family. Epsins 1 and 2 are constitutively and ubiquitous expressed proteins that function as molecular bridges required for clathrin-mediated endocytosis. Interestingly and in contract to epsins 1 and 2, epsin 3 was expressed exclusively and invariantly by collagen-activated keratinocytes, suggesting a novel role during epidermal repair. Moreover, we determined that similar intracellular pathway for induction of both genes following matrix contact. Our aims are: 1) to localize epsin 3 expression in vivo in wounded and pathologic tissues by in situ hybridization and immunohistochemistry; and 2) to characterize the molecular mechanisms understanding of altered cell:matrix interactions in epidermal wound repair.